Controllable vibration devices include controllable linear and rotary fluid dampers, mounts and the like. In particular, magnetorheological fluid devices include a magnetorheological fluid, i.e., a medium having magnetically soft particles suspended in a carrier fluid. One MR Fluid is described in commonly assigned U.S. Pat. No. 5,382,373 to Carlson et al. MR dampers are known and include both rotary and linear acting varieties. Rotary devices can be used as brakes, clutches and the like, for providing variable torque while linear-acting devices can be used for damping linear motion or for providing controllable dissipative forces along the damper's axis. For example, MR devices have been found useful in a wide variety of areas. MR dampers have been incorporated in vehicle engine mounts. One such device is taught in commonly assigned U.S. Pat. No. 5,398,917 to Carlson et al. In the mounting application, a rheology change of the MR fluid is used to control the engine motions by controlling the damping level therein. Other MR fluid devices are taught in the commonly assigned U.S. Pat. No. 5,277,281 and 5,284,330 to Carlson et al. which describe axially acting (linear) dampers and devices including sealless designs and in U.S. Pat. No. 5,492,312 to Carlson relating to Multi-Degree of freedom MR devices.
Copending applications Ser. No. 08/613,704 entitled "Portable Controllable Fluid Rehabilitation Devices" and Ser. No. 08/304,005 entitled "Magnetorheological Fluid Devices and Process of Controlling Force in Exercise Equipment Utilizing Same", both by Carlson et al., describe rotary dampers utilizing a controllable fluid for exercise and rehabilitation use. Copending applications Ser. No. 08/534,078 entitled "Controllable Seat Damper Systems and Control Method Therefor" and Ser. No. 08/639,139 entitled "Control Method for Semi-Active Damper" both by Catanzarite describe use and control of dampers.
A number of problems have emerged in developing viable controllable fluid dampers. First, the insertion of a valve within the piston of an MR damper as shown in FIG. 9a-9d of U.S. Pat. No. 5,284,330, generally may involve a great deal of machining: a single block of metal is machined out to provide space therein for the coil; then, MR fluid passageways are created by drilling or machining with very small diameter drills or cutting tools. Such machining is time-consuming and labor-intensive, resulting in a high cost part. Therefore, a valve construction is needed which is magnetically equivalent and easy to manufacture.
Second, providing electrical current to the controllable device to adjust the force properties of the device is difficult. The electrical connection of a power/current source to a moving member is addressed in commonly assigned U.S. Pat. No. 5,323,133. While this solution is suitable for some applications, the sealing of an electrical lead passing into a fluid chamber presents pressing difficulties. The sealing problem is aggravated in some applications, such as dampers, as the fluid pressures may be in excess of 500 psi. A cost-effective, and preferably high-pressure-handling solution for providing electrical power to vibration control devices, and in particular, to the electrically-controllable valves in dampers is needed. Further, easier and more manufacturable ways of making the internal electrical connections to the controllable-force components (e.g. controllable valves) are also needed.
Third, providing a proper seal between the piston rod and the aperture in the housing cap of which slidably receives the piston rod is particularly problematic, especially in an MR fluid device. The magnetically soft particles which are contained in fluid suspension within a MR fluid are for example, nominally between about 1 and about 6 microns, with a small percentage of the particles being outside of that range. These particles can readily work their way between the piston rod and its seal and, as a result of their abrasive nature, quickly abrade the seal. Therefore, a solution to the sealing problem in an MR damper is needed to effectuate longer life of the seals.
Fourth, a fluid accumulator to accommodate the fluid expansion and piston rod displacement in an damper, such as an MR damper, is needed. Prior art devices used accumulators of the floating-piston variety as taught in commonly assigned U.S. Pat. No. 5,284,330. MR fluid is displaced by the piston rod as it slidably enters the fluid chamber and also due to the fluid expansion/contraction resulting from thermal effects. The accumulator takes up, i.e., accommodates this fluid displacement/expansion. In an MR damper, the magnetically soft particles within the MR fluid can readily abrade any seal contained in the prior art floating-piston accumulator. It is important, then, to minimize contact between the seal and the magnetically soft particles and to minimize movement of the piston, to whatever extent is possible. This will, in turn, minimize wear. Furthermore, prior art high-pressure devices required a pressurizing valve, which is expensive. Therefore, there is a need for an inexpensive and durable accumulator system for MR devices. Any such accumulator system may have applicability to other dampers as well.
Fifth, another potential area of wear is at the interface between the piston and the damper body. The provision of an appropriate wear reducing surface and/or wear band is essential to meet the demanding life requirements for dampers. Further, it is desirable to have a wear system which will enhance the overall performance of the MR device. Therefore, there is a dire need for a wear reducing system for a MR damper.